1. Field of the Invention
This invention relates to a both-side image recording apparatus for recording images on both sides of a recording medium.
2. Description of the Prior Art
The conventional electrophotographic recording apparatus such as a copier or a laser printer has been constructed so that when it is desired to record images on both sides of a sheet, the sheet is first conveyed from a paper supply station to an image transfer station where a front surface toner image formed by an electrophotographic process is transferred to one surface of the sheet, and subsequently this toner image is fixed in a fixing station, whereafter the sheet is reversed by a reversing mechanism in the recording apparatus and transported back to the paper supply station and then a back surface toner image is formed on the other surface of the sheet through the same process. Therefore, the sheet conveyance route in the apparatus has been complicated and sheet jam has been liable to occur during the conveyance of the sheet, particularly, from the fixing station through the reversing mechanism to the paper re-supply station.
Also, where it is desired to record images on both sides of a sheet in the order of the original pages, the toner image of the first page is first formed on the front surface of the sheet and then the sheet is reversed. Subsequently, the sheet is transported back to the paper supply station and then the toner image of the second page is formed on the back surface of the sheet. Accordingly, the next sheet cannot substantially be reversed until the preceding sheet is completely reversed by the reversing mechanism in the recording apparatus and passes therethrough, and this has led to the disadvantage that the time efficiency (throughput) for conveyance is reduced.
To prevent this throughput from being reduced, there is a method whereby several odd pages corresponding to the front surfaces are formed on the front surfaces, whereafter even pages corresponding to the back surfaces are successively formed on the back surfaces. This method, however, requires a reversing mechanism for containing therein several pages of sheets printed on one side thereof and re-supplying them in the order of the original pages. This has led not only to the disadvantage that the apparatus becomes bulky and expensive, but also to the disadvantage that the reliability of sheet conveyance is further reduced.
There is also a both-side recording apparatus of the type which uses two printers exclusively for one-side recording and in which the two printers are series-connected together by a switch back type sheet reversing device so that one of the printers executes printing on the front surface of a sheet and the sheet is then conveyed to the other printer through the reversing device, after which the other printer executes printing on the back surface of the sheet. In such a both-side recording apparatus, the right and left ends of the sheet relative to the direction of movement of the sheet are not changed before and after the sheet reversing device, while the leading and trailing end edges of the sheet are changed and therefore, when both-side printing is effected, the tops and bottoms of the images on the front and back surfaces of the sheet are reversed relative to each other. For this reason, when an image is recorded on a photosensitive medium by the use of a laser beam, it has been necessary to reverse the top and bottom of the image or to turn breadth to length. Also, in the switch back type sheet reversing device, the sheet is once stopped and then moved in the opposite direction, and this has led not only to a reduced throughput but also to occurrence of jams which may result from even slight waving or curling of the sheet and thus, to many problems in sheet conveyance.